Hydraulic vehicle lifts are available in a variety of forms including two post, four posts, inground, parallelogram, scissor and portable type.
Generally speaking such vehicle lifts move from a first ground contacting position to a second raised position whereby a vehicle driven unto the lift may be raised from the ground to a raised position permitting wheel alignment, oil change, and other work to be conducted on the vehicle.
Such vehicle lifts generally include a pair of spaced-apart support platforms or rails for supporting the wheels or frame of a vehicle. These support platforms are adapted to be moved by hydraulic cylinders which raise and lower the support platforms as stated. Some vehicle lifts include one cylinder while others may include two cylinders where one of said cylinders is adapted to move one of the support platforms and the other cylinder is adapted to move the other support platform.
Accordingly when using a pair of hydraulic cylinders to move one pair of spaced-apart platforms, it is necessary that the cylinders with the support platforms move in a uniform fashion. If one of the support platforms does not move in unison with the other, a dangerous situation can occur whereby one of the support platforms or tracks is either higher or lower than the other which can cause the vehicle to fall off the lift from a raised position and produce damage to the car and potential hazard to any individuals in the vicinity.
Accordingly various attempts have heretofore been made in the prior art in order to equalize the ascent and descent of the first and second cylinder which moves a first and second vehicle support. Such prior art devices include manually operated circuitry which must be manually operated in order to attempt to adjust the hydraulic cylinders and therefore the height levels of the vehicle supports. However, manual adjustment is prone to error and if the wrong buttons are pushed may actually worsen the situation.
Other prior art devices are shown for example in U.S. Pat. No. 5,833,260 which includes a gyro leveling sensor mounted between and below the level of the support tracks with data transmitted to an assembly of display lights which indicate a high portion of the unit. The unit may then be leveled by initiating hydraulic pressure or release of pressure on one of the link support hydraulic cylinders disclosed therewith.
Another equalizing system is shown in U.S. Pat. No. 5,783,755 which illustrates a lifting device that has a carriage supported by a chain which passes over a sprocket-wheel disposed to rotate about an axis and includes an equalizer system that reduces variations in the measurement, by a load cell, of a load supported by the carriage.
Another arrangement is shown in U.S. Pat. No. 5,800,000 which provides a load adjusting device for use with a lifting unit where the device includes a load spreader or spreader bar supported from a single lift point lift.
Such prior art devices as well as others utilized in vehicle lifts are relatively complicated.
It is an object of this invention to provide an improved method and apparatus for monitoring and controlling the uniform movement of the support platforms in a vehicle lift.